Subaerial gutter marks. Raindrop impressions, scour marks and other sedimentary structures, Silurian tymochtee dolomite, Waterville, Ohio

Abstract

Field work was carried out on a four meter thick sequence of unfossiliferous Silurian Tymochtee Dolomite along the southeastern margin of the Silurian Michigan basin. Bedding plane exposures are common. The studied section contains a swale, gutter marks, scour marks, anhydrite molds, raindrop impressions, flat-pebble conglomerate, and ripple marks. Rocks with raindrop impressions formed in a subaerial environment. Many of the gutter marks form linear arrays. They originated as independent rivulets in a subaerial environment during a rain storm. No evidence of sheet flow has been found. The raindrop impressions associated with the gutter marks formed contemporaneously with the formation of the latter or shortly after. The present report documents the only known presence of gutter marks and raindrop impressions found in any Silurian strata anywhere within Michigan, Ohio and Indiana. Gutter marks formed in a subaerial environment may be more common than realized previously. Lastly, this paper argues that the size, shape, patterns, and presence of raindrop impressions has environmental significance beyond that of indicating subaerial exposure of a sediment.